The present application claims priority to Application No. 101 41 439.0, filed in the Federal Republic of Germany on Aug. 23, 2001, which is expressly incorporated herein in its entirety by reference thereto.
The present invention relates to a tripod joint for two ends of a drive shaft.
Tripod joints are used, for example, as half shafts of motor vehicles. In this case, the tripod joints are used for transmitting drive torques between two drive elements of a drive train. The tripod joints permit relative displacement and relative pivoting of the drive elements to be compensated for. For the use in the case of half shafts of a motor vehicle, relative movements of this type are caused by spring deflections of the vehicle wheels.
U.S. Pat. No. 4,619,628 describes a tripod joint having a joint outer part and a joint inner part held in the joint outer part. The joint inner part has a tripod star having pins with a ball body. The ball bodies are accommodated pivotably in a partially spherical universal ball joint of a pressure element and are therefore mounted pivotably with respect to the pressure element. The pressure element has a running surface on the side facing away from the ball body. Rolling bodies are arranged between the running surface and a mating surface of the joint outer part, in order to transmit the drive torque.
It is an object of the present invention to provide a tripod joint which is optimized with regard to the forces which occur in the region of the running surfaces, of the mating surfaces and of the rolling bodies.
The above and other beneficial objects of the present invention are achieved by the tripoid joint as described herein.
Investigations have shown that, particularly when large drive torques need to be transmitted, elastic deformation occurs in the components which form the mating surfaces and the running surfaces.
By way of example, if a force is introduced centrally through the ball body, that subregion of the running surface which projects in the running direction bends as a consequence of the reaction forces exerted by the rolling bodies. As a consequence of this, the distance between the running surface and the associated mating surface is increased in this subregion (in the micrometer range). As a consequence of this, the force to be transmitted decreases in the outer subregions of the running surface. This leads to the force being distributed inhomogeneously over the running surface. With a predetermined maximum surface pressure in the region of maximum forces, the maximum force which can be transmitted is thus not utilized in the outer subregions, while an optimum force distribution is achieved only for small drive torques.
According to the present invention, the running surface of the pressure element is curved in the running direction of the rolling bodies. The curvature is such that the distance between the running surface and the planar mating surface decreases in the direction of the outer subregions. The curvature is configured such that, when large drive torques need to be transmitted, an approximately planar running surface is produced, so that the forces to be transmitted are approximately equal on all the rolling bodies.
In consequence, all the rolling bodies may be stressed to a uniform extent, thus resulting in improved running characteristics and reduced wear. The surface pressures on the running surface and on the mating surface are likewise optimized, so that the wear on these operating surfaces may also be reduced. The drive torques which may be transmitted may be increased for the same component dimensions. According to the present invention, a non-uniform force distribution is therefore accepted for small drive torques, while an optimum force distribution may be achieved for large drive torques. The pressure element may be designed to be thinner, and it is possible to deliberately accept elastic deformation of the pressure element, which may be compensated for by the curvatures for large loads. This may result in a more compact tripod joint.
The running surface of the pressure element may include entry inclines or radii in the entry region of the rolling bodies. This makes it possible to improve the threading of the rolling bodies into the running surface, and hence into the force flow. In addition to reducing the mechanical stress on the components involved, this may result in a reduction in sudden force changes, which occur as a result of the threading-in process, during movement or pivoting of the tripod joint.
Exemplary embodiments of the tripod joint according to the present invention will be explained in greater detail below with reference to the drawings.